Video communication service is a multimedia service that synthesizes information such as voice, image and data etc. and makes long haul transmission of them. A video communication service may be a videoconference and includes three types of information: image, voice and data. A videoconference service can be seen as a conventional conference television service and is one kind of video communication services. The videoconference is one kind of communication modes for a conference held at two or many different sites. This telecommunication mode uses television technology and equipment, and through transmission channel to serve a conference.
Video communication service makes it is possible that when people communicate at different sites, they can hear voice of each other and can see images of each other. This enhances real feelings, sincere feelings and at site feelings of communication. Video communication service is used in military, politic, economic, education and health fields etc., and has reality, high efficiency and real time advantages. Video communication service provides an effective mean for communication, management and collaboration of decision making etc.
As shown in FIG. 1, in general a video communication service system is consisted of video communication terminals, transmission channels and multipoint control units (MCU), which will be described in the following, respectively.
A video communication terminal samples, compress codes and multiplexes image, voice and relating data signal, which happen at a conference site, then sends to a transmission channel. At the same time, the video communication terminal sorts, decodes a received video communication service signal and returns to the image, voice and data signal of the conference site where the signals originally happen. Further, the video communication terminal sends conference control signal (such as apply for speaking, apply for the control of a conference etc.) to a MCU, and executes control commands from the MCU for the site. The video communication terminal also makes capability exchange and mode switching with the MCU. A capability exchange means a procedure that both sides of the communication exchange the service capability, which they support respectively.
Physically, A transmission channel can be optical fiber, cable, microwave or satellite mode etc. The communication networks that are commonly used for video communication service are a public switcher telephone network (PSTN), a packet switched public data network (PSPDN) and a digital data network (DDN) etc. At present, broadband network based on ATM technology is developed rapidly, this gives video communication service a wider development area, such as ISDN network, IP network and IQ network. Further more, as the ISDN network and Internet are increasingly popular, video communication service has a better condition to spread rapidly general people.
There are different communication protocols for different communication networks. The H.323 is a member of H.32X family developed by ITU-T. Other members of H.32X family are used in different networks for implementing multimedia communication, such as H.324 for SCN, H.320 for ISDN, H321 and H310 for B-ISDN and H.322 for LAN with QOS guarantee.
The H.323 recommendation is a standard for a multimedia conference system (also called H.323 conference system) based on a public switched network (PSN). The H.323 conference system supposes that the network which it bases on is a network without providing QOS guarantee. Along with the rapid development of IP network, the H.323 standard is mainly applied in IP network. An important purpose of H.323 standard is to interconnect with multimedia services on other networks, and this is performed by a gateway. In H.323 network, one important optional component is gatekeeper (GK), which can be understood as a “brain” of the network and is a focus of all internal calls in the H.323 network.
As shown in FIG. 1, MCUs are the control kernel of a video communication service system. When terminals attending a conference are more than two, they must be controlled by a MCU. All terminals are connected to a MCU with standard interface. A MCU implements exchange and mixture of image and voice, and all conference control functions according to the international standards: H.221, H.242, H.243 and T.120 etc.
In present technology, a video communication service is implemented that before a conference has been convened, resources must be pre-allocated in MCUs between all sites of the conference. This means that before convening a videoconference, a conference and its sites are defined in a MCU, the conference is controlled by the MCU, and resources are distributed accordingly. Once resources are satisfied, the conference can be convened. Obviously, this kind of operation mode cannot satisfy a requirement of video communication service providing publicly. The disadvantages are as follow. First, from the service provider point of view, it is necessary to have a special operator to control the MCU, to define a conference and sites, to manage the conference. This will greatly decrease efficiency of a video communication service network and limit profit of a video communication service system. Secondly, from the user point of view, a user must take a phone call or go to a video communication service office to schedule a conference, then the staffer of the office informs a MCU operator to call the conference at the scheduled time. This not only cannot provide real time service, but also less of security.